The present invention relates to implantable defibrillation systems, and more particularly to an implantable defibrillation system which employs a multiple electrode configuration and requires lower energies to defibrillate a heart.
There is a continuing effort in the field of implantable cardioversion/defibrillation to minimize the energy required to effectively cardiovert/defibrillate a patient's heart. Some of this effort has focused on the structure and placement of cardioversion/defibrillation electrodes to maximize the efficiency with which energy is delivered to the heart and to minimize the complexity of the surgical procedure required to implant or otherwise place the electrodes in or about the heart.
For example, U.S. Pat. No. 4,827,932 to Ideker et al. relates to epicardial implantable defibrillation patch electrodes. A first patch is designed to fit over the right ventricle and a second patch is designed to fit over the left ventricle with a substantially uniform gap being provided between borders of the patches. The gap is of sufficient width to prevent shunting of current between the two patches. The electrodes disclosed in this patent are described as achieving a uniform voltage gradient throughout the entire ventricular mass.
As another example, U.S. Pat. No. 4,603,705 to Speicher et al. discloses an intravascular multiple electrode catheter for insertion into the heart through the superior vena cava. The catheter supports a distal electrode for sensing and pacing, an intermediate electrode for sensing, pacing and cardioverting, and a proximal electrode for sensing and cardioverting. A patch electrode may be used in conjunction with the catheter.
Other efforts have been directed to particular types of cardioversion/defibrillation waveforms and techniques for delivering the waveforms to the heart. For example, U.S. Pat. Nos. 4,637,397 to Jones et al., 4,800,883 to Winstrom, and 4,821,723 to Baker, Jr. et al. are representative of patents disclosing systems and techniques for generating multi-phasic defibrillation waveforms. Another defibrillation waveform variation is disclosed in U.S. Pat. No. 4,768,512 to Imran which relates to a high-frequency truncated exponential waveform.
Elaborate defibrillation delivery techniques have been developed in an attempt to minimize the energy required by providing uniform voltage gradients throughout the myocardium. U.S. Pat. Nos. 4,548,203 and 4,708,145 to Tacker, Jr. et al., and U.S. Pat. Nos. 4,641,656 and 4,774,952 to Smits disclose a sequential orthogonal pulse delivery regime in which two pairs of opposing electrodes are implanted orthogonally to each other. A first shock is delivered between the first pair of electrodes and a second shock is delivered between the second pair of electrodes. This technique is described in these patents as equalizing the current distribution across the heart and concentrating the current in the muscular areas of the heart.
Yet another variation of the aforementioned systems is that disclosed in U.S. Pat. No. 4,727,877 to Kallok. The Kallok patent discloses a transvenous defibrillation lead system including a first catheter supporting a first electrode pair comprising a right apex ventricular electrode and a superior vena cava electrode. A second electrode pair is provided, comprising a ventricular tip electrode at the end of the first catheter and a coronary sinus electrode supported by a transvenous superior vena cava right atrial lead. A first pulse is delivered to the first pair of electrodes between the ventricular apex and the vena cava, and a preset time interval later, a second pulse is delivered to the second pair of electrodes between the ventricular apex and the coronary sinus. The patent states that a spatial summation of the sequential shocks occurs resulting in a reduction of the energy required to defibrillate the heart as compared to prior systems.
Rather than attempt to achieve uniform gradients throughout the myocardium, a technique has been developed which ensures that substantially all of the myocardium is placed above a critical voltage gradient so as to effectively countershock a fibrillating heart at low energies.